1. Field of the Invention
The present invention relates to economical and technically available processes for the extraction of ethanol from active fermentations and the further concentration of that extract to higher concentrations to permit economical further processing of the ethanol by distillation, pervaporation or other concentration processes. The process is intended to be run on a continuous basis during the fermentation process and to remove ethanol at a removal rate to keep the fermentation in its optimal production phase. Ethanol for all fermentation has an inhibitory effect on the organisms and will eventually kill the organisms if high enough levels are produced. Using this process the fermentation rates can be increased up to 20 fold and the resultant concentrated ethanol water mixtures can be economically processed to a highly concentrated ethanol product.
2. Background Information
The United States is increasingly dependent on imported energy to meet our personal, transportation, and industrial needs. The U.S. imports 65% its petroleum needs today. By 2030, the Energy Information Administration (EIA) projects the U.S. will import 70% of its petroleum. And oil prices are not expected to ease soon. EIA estimates oil prices will hover near or above $100/barrel through 2030. Record oil and gas prices in 2008 underscore the need for energy independence by eliminating that volatility in the market caused by instability and conflict in oil-producing parts of the world.
To address this concern, and building upon the Energy Policy Act of 2005 (the first comprehensive energy bill in more than a decade), President Bush announced his Advanced Energy Initiative in the 2006 State of the Union Address with focus on reducing U.S. gasoline usage by 20% in the next ten years-Twenty in Ten (Strengthening America's Energy Security). This goal will be achieved by 1) increasing the supply of renewable and alternatives fuels by setting a mandatory fuels standards to require 35 billion gallons of renewable and alternative fuels in 2017-nearly five times the 2012 target now in the law, and 2) Reforming and modernizing corporate average fuel economy (CAFÉ) standards for cars and extending the current light truck rules.
As a domestic, renewable source of energy, ethanol can reduce our dependence on foreign oil and increase the United States' ability to control its own security and economic future by increasing the availability of domestic fuel supplies. In 2006, the production and use of ethanol in the U.S. reduced oil imports by 170 million barrels, saving $11 billion from being sent to foreign and often hostile countries (Source: LECG, LLC December 2006). This ethanol is typically fuels and traditional uses like livestock and poultry feed, food processing and exports. Therefore, efficiently producing ethanol from cellulosic feedstock would provide large, new sources of raw materials for the production of renewable fuel. However, the cellulosic ethanol is not commercially produced in the United States today.
A major problem, which has long plagued the ethanol fermentation process, is that the yeasts and bacterial used to produce ethanol have their growth inhibited and they can be killed with the very ethanol that they are producing. This problem will increase, as fermentation of alternative feedstock other than corn or sugar cane is required. All yeasts and bacteria that can ferment the alternate feedstock have a much lower tolerance to ethanol.
If the biomass contains or can be converted to glucose it can be fermented as the corn ethanol process. The standard fermentation yeast used today is Saccharomyces cerevisiae If the biomass conversion yield other sugar types the fermentation process must use non-standard yeasts and bacteria to ferment the sugar to ethanol. Lactose is a good example of a non-glucose sugar in milk that is a waste product of the cheese industry. It can be converted to ethanol but the process shows much ethanol inhibition with the normal fermentation yeast Kluyveromyces fragilis (Vienne and Stockar 1985) (Grubb and Mawson 1993) or with Recombinant S. cerevisiae (Guimaraes P, Klein J, Doimengues. L, and Teixeira, J (2005).
Generally, less than half of the alternate feedstock materials will convert to glucose. The other sugars are a mix of difficult to ferment hexose and pentose sugars. Some of the fermentation alternative types of microorganisms that have potential to convert the other sugars to ethanol are Pichia stipitis, recombinant Escherichia coli, Zymomonas mobilis, various recombinant Saccharomyces various species, Candida shehatae, Pachysolen tannophilus, etc. Most or all of these fermentation alternatives experience significant ethanol inhibition at low ethanol concentrations.
The inhibition of cell growth at low ethanol concentration delays fermentation times greatly. Conversion of sugars to ethanol can take place in non-growing cells, however higher levels of ethanol will also stop that conversion.
Ethanol concentration inhibition also has the effect of inhibiting the enzymatic conversion of cellulose and hemicelluloses to fermentable sugars during fermentation by organisms of added external enzymes. Ethanol has been proven to be inhibitory of the cellulases enzymes (Wu and Lee, 1997). Levels are very low in the 2%-3% v/v range (Jorgensen, Vibe-Pedersen, Larsen and Felby, 2006).
Ethanol removal from fermentation broths is possible and much study has been given to it to date. However no processes are commercially viable at this time. The main method for ethanol removal during fermentation at this time has been the use of hydrophobic pervaporation membrane processes. Earlier methods of continuous ethanol removal by stripping with CO2 (U.S. Pat. No. 5,141,861 1992 Clark Dale) or other gasses, solvent extraction with a raffinate solvent, (U.S. Pat. No. 4,517,298 1985 Tedder), Zeolite or other resin sorbents (U.S. Pat. No. 4,420,561 1983 Chen), Extraction and Distillation (U.S. Pat. No. 4,448,644 1984 Foster), Packed column counter current water/gas stripping (Taylor, Kurantz, et all, 1997), tower fermentors with striping (Scott and Cooke, 1995) and many other methods have been tried with no commercial success.
Many studies have also been done on the use of hydrophobic pervaporation membranes in batch and continuous fermentations with some success also. The particularly good news is that ethanol inhibition is reduced. Improvements in ethanol productivity were obtained by 1.58 and 1.86 times. (Zhang Wei, Yu Xingju and Yuan Quan 2000) Other studies show that the ethanol production rate fermenting lactose to ethanol can be increased from 1-2 g/L/Hr to 10 g/L/Hr removing ethanol in a continuous system. (Lewandowska and Kujawski 2007) A typical base rate for corn ethanol production rate is 1-3 g/L/Hr.
O'Brien of the USDA Eastern Regional Research Center has studied the process and economics in general since 1999. In his 1999 model of the fermentation-pervaporation, process continuously higher fermentation conversion and ethanol production rates can be increased for the normal fermentation by 12 times. He therefore needed on one twelfth the reactor volume of the normal fermentation. Pervaporation increased the ethanol concentration from 7.1% in the pervaporation feed to 42% ethanol in the pervaporation permeate. The economics of doing this was not positive however. The total cost to produce of amortized capitol and operating costs were $0.192 for the fermentation/pervaporation process vs. $0.182 for the base ethanol plant. (O'Brien et al. 2000)
The problem with using a hydrophobic pervaporation/fermentation system is three fold. First, the costs of the membranes are still very high. Second, the process requires high vacuums and refrigeration to condense the ethanol. Third the performance drop off from the membranes can be significant due to fouling during operation. Fermentation by products, such as succinic acid and glycerol, can cause membrane fouling. (Ikegami et all, 1997, 2000)
Applicants have devised an economical process for recovering ethanol from an active fermentation broth that is an improvement over the existing technologies.